Method and apparatus for controlling power converter with inverter output filter

ABSTRACT

Power converters and methods are presented for driving an AC load connected through an intervening filter circuit, in which at least one filter current or voltage signal or value is determined according to feedback signals or values representing an output parameter at an AC output of the power converter, and AC electrical output power is generated at the AC output based at least partially on the at least one filter current or voltage signal or value.

BACKGROUND

Power conversion systems are used to generate and provide AC outputpower to a load, such as a single or multi-phase AC motor driven by aninverter stage of a motor drive power converter. Pulse width modulated(PWM) output inverters provide output currents and voltages including anumber of pulses, and output filters are sometimes employed between thepower converter and the driven load to reduce the high frequency contentcaused by pulse width modulation. The presence of the output filterbetween the power conversion system and the load, however, makesaccurate control of the voltages and/or current provided to the loadmore difficult, as the power delivered to the load is different fromthat delivered to the input of the filter. In particular, the outputinverter stage may be controlled according to feedback signals measuredat the inverter output terminals, and these feedback values may notrepresent the currents or voltages ultimately provided to the load.Feedback sensors can be provided at the load itself for directmeasurement of the load parameters, but this increases system cost, andmay not be possible in all applications. Accordingly, there is a needfor improved power conversion systems and techniques for driving a loadthrough an intervening filter circuit by which load control can befacilitated without requiring extra feedback sensors positioned at theload and without significant modification to the inverter control systemof the power converter.

SUMMARY

Various aspects of the present disclosure are now summarized tofacilitate a basic understanding of the disclosure, wherein this summaryis not an extensive overview of the disclosure, and is intended neitherto identify certain elements of the disclosure, nor to delineate thescope thereof. Rather, the primary purpose of this summary is to presentvarious concepts of the disclosure in a simplified form prior to themore detailed description that is presented hereinafter.

Power conversion systems and operating methodologies are disclosed forpowering a load through an intervening filter circuit, which findutility in association with motor drives or other forms of powerconverters, and may be employed to power or drive any form of load, suchas a single or multi-phase permanent magnet synchronous motor (PMSM).These techniques may be successfully implemented to facilitate improvedcontrol over driven motors and other loads without significant change toinverter controller configuration and without requiring the addition ofdirect feedback sensors at the load.

Power converters are disclosed, which include an inverter and anassociated controller that determines one or more filter currents orvoltages representing one or more filter capacitor currents or filterinductor voltages of the intervening filter circuit, based on one ormore inverter output feedback signals or values. The controller providesinverter switching control signals based at least in part on the filtercurrents or voltages. In certain embodiments, the power converter may bea motor drive, with the inverter providing output power to drive a motorload through the intervening filter circuit.

In certain embodiments, the controller computes a current setpoint basedon a desired velocity and motor velocity, and computes a filtercapacitor current value according to the motor velocity, a compensatedvoltage reference, and a filter capacitance value. The controllercomputes a compensated current setpoint value based on the currentsetpoint and the filter capacitor current value, and provides theinverter switching control signals based at least partially on thecompensated current setpoint.

In various embodiments, the controller computes a voltage referencebased on the compensated current setpoint and on output current feedbackrepresenting an output current at the inverter output. The controllercomputes a feed forward voltage value based on the output currentfeedback, the motor velocity, the filter capacitor current value, and ona filter inductance value. The controller computes a compensated voltagereference value based on the voltage reference and the feed forwardvoltage reference, and provides the inverter switching control signalsbased at least partially on the compensated voltage reference value.

Methods are provided for controlling an AC electric motor connected to amotor drive through an intervening filter circuit. The method includesdetermining at least one filter current or voltage representing a filtercapacitor current or filter inductor voltage of the intervening filtercircuit based on at least one motor drive output feedback signal orvalue representing an output current at the AC output of the motordrive, and generating AC electrical output power at the motor driveoutput at least partially according to the filter current or voltage.

In certain embodiments, the method includes determining a filtercapacitor current value representing current flowing in a filtercapacitor of the intervening filter circuit based on a motor velocitysignal or value, a compensated voltage reference value, and a filtercapacitance value. The compensated current setpoint value is computedbased at least partially on the filter capacitor current value, and theinverter switching control signals are provided at least partiallyaccording to the compensated current setpoint value.

Certain embodiments of the method further include determining at leastone current setpoint signal or value based at least partially on adesired motor velocity and the motor velocity signal or value, as wellas computing the compensated current setpoint value based on the currentsetpoint value and the filter capacitor current value.

In certain embodiments, moreover, the method includes computing avoltage reference value based on the compensated current setpoint valueand at least one inverter output current feedback signal or valuerepresenting an output current at the inverter output. In addition, afeed forward voltage reference value is computed based on the inverteroutput current feedback signal(s) or value(s), and a compensated voltagereference value is determined based on the voltage reference value andthe feed forward voltage reference value, with the inverter switchingcontrol signals being provided at least partially according to thecompensated voltage reference value.

Non-transitory computer readable mediums are provided with computerexecutable instructions for controlling an AC electric motor connectedto a motor drive through an intervening filter circuit according to thedescribed methods.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description and drawings set forth certain illustrativeimplementations of the disclosure in detail, which are indicative ofseveral exemplary ways in which the various principles of the disclosuremay be carried out. The illustrated examples, however, are notexhaustive of the many possible embodiments of the disclosure. Otherobjects, advantages and novel features of the disclosure will be setforth in the following detailed description when considered inconjunction with the drawings, in which:

FIG. 1 is a simplified schematic diagram illustrating a motor drive withan inverter controller configured to control motor current based onsensed inverter output current signals or values while compensating forthe presence of an output filter between the motor drive output and adriven permanent magnet synchronous motor (PMSM);

FIG. 2 is a schematic diagram illustrating further details of theinverter controller of FIG. 1;

FIG. 3 is a schematic diagram illustrating further details of a filtercurrent calculation component, a current reference component, as well asa current proportional-integral (PI) feed forward component of theinverter controller of FIGS. 1 and 2; and

FIG. 4 is a flow diagram illustrating a process for driving a motor loadthrough an intervening filter circuit.

DETAILED DESCRIPTION

Referring now to the figures, several embodiments or implementations arehereinafter described in conjunction with the drawings, wherein likereference numerals are used to refer to like elements throughout, andwherein the various features are not necessarily drawn to scale.

Power converters and methods are disclosed for controlling a loadconnected through an intervening filter circuit, by which improvedcontrol may be facilitated without the addition of extra feedbacksensors or extensive modifications to inverter output control schemes.These concepts are hereinafter described in the context of a motor drivepower converter controlling an AC permanent magnet synchronous motor(PMSM), although the invention is not limited to motor drive type powerconverters, or to PMSM type loads. The described embodiments utilizeonly the measurements of inverter output currents (without directlysensing voltages and/or currents at the driven motor load), and hencefacilitate the addition of an intervening filter to any motordrive/driven motor system without significantly impacting cost and/orcomplexity. Consequently, the presently disclosed power conversionsystems and methods present a significant advance over attempts tointroduce additional cascaded control loops, adaptive full-orderobservers, and/or other complicated processing components or steps intoa PMSM inverter vector control architecture, and also facilitateimproved motor control without requiring extra hardware or major changesin the control structure for a conventional PMSM drive or other type ofpower conversion system.

Disclosed examples include a simple control scheme for PMSM drives withan inverter output filter considering filter dynamics, without use ofany additional hardware. Various embodiments, moreover, may be employedin a variety of power conversion systems, including without limitationvoltage source AC drives equipped with an output filter, or powerconverters installed for driving a motor through an intervening outputfilter, whether the intervening filter circuit is integral to the driveor not. The disclosed apparatus and methods thus provide a simplesolution to consider output filter dynamics with improved performancewithout major hardware or software changes on an existing drive. Thedisclosed techniques, moreover, require only the measurements of theinverter output current without additional sensors to provide directvoltage and/or current values from the driven load, and thus, a filtercan be easily added to an existing drive without any hardwaremodifications. In certain embodiments, moreover, an improved currentreference generator is provided, and a new feedforward control isprovided for a current loop proportional/integral (PI) controller in aninverter controller.

FIG. 1 shows a permanent magnet synchronous motor (PMSM) drive 40 withan inverter 46 and an inverter controller 100 configured to controlcurrent of a driven motor load 20 based on sensed inverter outputcurrent signals or values i_(u), i_(v), i_(w), representing outputcurrents flowing at the AC output 46B of the inverter 46. The controller100, moreover, is configured to compensate for the presence of an outputfilter 30 connected between the motor drive output 46B and the drivenmotor 20.

As seen in FIG. 1, the drive 40 receives single or multiphase AC inputpower from a power source 10 and converts this to a DC bus voltage usinga rectifier 42 providing a DC output voltage to a DC link circuit 44having a capacitor C. The rectifier 42 can be a passive rectifierincluding one or more diode rectifier components, or may be an activefront end (AFE) system with one or more rectifier switching devices(e.g., IGBTs, etc.) and an associated rectifier controller (not shown)for converting input AC electrical power to provide the DC bus voltagein the link circuit 44. Other configurations are possible in which thedrive 40 receives input DC power from an external source (not shown) toprovide an input to the inverter 46, in which case the rectifier 42 maybe omitted. The DC link circuit 44, moreover, may include a singlecapacitor C or multiple capacitors connected in any suitable series,parallel and/or series/parallel configuration to provide a DC linkcapacitance across the inverter input terminals 46A. In addition, whilethe illustrated motor drive 40 is a voltage source converterconfiguration including one or more capacitive storage elements in theDC link circuit 44, the various concepts of the present disclosure maybe implemented in association with current source converterarchitectures in which a DC link circuit 44 includes one or moreinductive storage elements, such as one or more series-connectedinductors situated between the source of DC power (e.g., rectifier 42 orexternal DC source) and the input 46A of the inverter 46. In otherpossible implementations, the motor drive 40 includes a direct DC inputto receive input power from an external source (not shown), and incertain embodiments the rectifier 42 and DC link circuit 44 may both beomitted.

The inverter 46 includes a DC input 46A having first and second (e.g.,plus and minus) terminals connected to the DC link circuit 44, as wellas a plurality of switching devices S1-S6 coupled between the DC input46A and the motor drive AC output 46B. In operation, the inverterswitching devices S1-S6 are actuated by inverter switching controlsignals 102 provided by the controller 100 in order to convert DCelectrical power received at the DC input 46A to provide AC electricaloutput power at the AC output 46B. The filter circuit 30 receives the ACoutput from the inverter 46 of the motor drive 40, and is thereafterconnected to the phase windings of the motor load 20. Althoughillustrated as driving a permanent magnet synchronous motor 20, themotor drive 40 can be employed in connection with other types of ACmotor loads 20 and/or other forms of power converters to drive non-motorloads 20 using an output inverter 46. In the illustrated system,moreover, one or more feedback signals or values may be provided fromthe motor 20 itself, including a motor (e.g., rotor) position or anglesignal θ_(r) and a motor speed or velocity signal w, although not astrict requirement of all embodiments of the present disclosure. In thisregard, the motor drive 40 in certain embodiments implements a motorspeed and/or position and/or torque control scheme in which the invertercontroller 100 selectively provides the switching control signals 102 ina closed and/or open-loop fashion according to one or more setpointvalues such as a motor speed setpoint ω_(r)*. In practice, the motordrive 40 may also receive a torque setpoint and/or a position (e.g.,angle) setpoint, and such desired signals or values (setpoint(s)) may bereceived from a user interface and/or from an external device such as adistributed control system, etc. (not shown).

As seen in FIG. 1, moreover, the motor drive 40 is connected to the load20 through an intervening filter circuit 30. In the illustrated example,the filter 30 is an “L-C” configuration in which each of the powerconverter output lines is connected to the motor through aseries-connected filter inductor L_(f), with a corresponding filtercapacitor C_(f) connected between the corresponding motor line and acommon connection point (a neutral of a Y-connected set of filtercapacitors C_(f) in the illustrated example). Other implementations arepossible in which the filter capacitors C_(f) are connected in a “Delta”configuration. In the illustrated (Y-connected) configuration, moreover,the filter circuit neutral point can be optionally connected to acircuit ground or other, connection point associated with the motordrive 40, although not a strict requirement of the present disclosure.The disclosed apparatus and techniques can be employed in connectionwith other forms and types of filter circuits 30, including withoutlimitation L-C-L circuits, etc., of which behavior can typically bemodeled as a second order system. As seen in FIG. 1, moreover, the phasecurrents i_(m) provided to the motor load 20 from the output of thefilter circuit 30 will control the operation of the motor 20, whereasfilter currents i_(c) (i.e., filter capacitor currents) may flow in thefilter capacitors C_(f) and non-zero voltages v_(L) (i.e., filtervoltages) may develop across one or more of the filter inductors L_(f),whereby simple closed-loop control based on measured inverter outputcurrent signals or values i_(u), i_(v), i_(w) may result in less thanoptimal operation of the driven load 20. At the same time, however,directly measuring the motor currents i_(m) and/or motor voltages wouldrequire additional hardware and cabling, which may not be economicallyfeasible or technically possible in certain applications.

Referring also to FIGS. 2-4, the drive 40 includes one or more currentsensors configured to measure, sense, or otherwise detect at least oneinverter output feedback signal or value (e.g., output currents i_(u),i_(v), i_(w)) which represent the output current at the AC output 46B ofthe inverter 46, and the controller 100 is programmed or otherwiseconfigured to determine at least one filter current or voltage signal orvalue representing a filter capacitor current is or filter inductorvoltage v_(L) of the intervening filter circuit 30 based at least inpart on the inverter output feedback (e.g., i_(u), i_(v), i_(w)), and toprovide the inverter switching control signals 102 at least partiallyaccording to the filter current or voltage signals or values. In thismanner, the inverter controller 100 accommodates the presence of thefilter circuit 30 between the motor drive output 46B and the drivenmotor load 20, without requiring addition of external sensors. Moreover,the controller 100 can implement an otherwise conventional motor controlscheme without having to provide complicated observer components orotherwise modifying the closed loop control for driving the motor load20. The controller 100 and the components thereof may be any suitablehardware, processor-executed software, processor-executed firmware,logic, or combinations thereof that are adapted, programmed, orotherwise configured to implement the functions illustrated anddescribed herein. The controller 100 in certain embodiments may beimplemented, in whole or in part, as software components executed usingone or more processing elements and may be implemented as a set ofsub-components or objects including computer executable instructions foroperation using computer readable data executing on one or more hardwareplatforms such as one or more computers including one or moreprocessors, data stores, memory, etc. The components of the controller100 may be executed on the same computer processor or in distributedfashion in two or more processing components that are operativelycoupled with one another to provide the functionality and operationdescribed herein.

FIGS. 2 and 3 illustrate further details of a nonlimiting embodiment ofthe inverter controller 100, and FIG. 4 illustrates a process fordriving a motor load 20 through an intervening filter circuit 30 whichmay be implemented in whole or in part via the inverter controller 100in certain embodiments. As seen in FIG. 2, the inverter controller 100receives a desired motor velocity signal or value ω_(r)* (e.g., from auser interface or other setpoint source) along with a motor velocitysignal or value ω_(r). The velocity signal or value ω_(r) can beobtained from any suitable source, and may be provided through, orderived from, feedback signals from the motor load 20 in certainembodiments, although not a strict requirement of the presentdisclosure. In addition, the controller 100 receives phase currentfeedback signals or values i_(u), i_(v), i_(w) representing the outputcurrents at the AC output 46B of the motor drive 40 (e.g., from outputcurrent sensors as seen in FIG. 1), and a DC bus voltage signal or valueV_(dc). The operating parameters and variables illustrated and describedherein can be one or both of signals and/or values (e.g., digitalvalues), and the controller 100 and other components of the motor drive40 may include various analog-to-digital converters as well asdigital-to-analog conversion components. Moreover, various parameterscomputed and used by the controller 100 and the components thereof maybe represented in a synchronous reference frame (e.g., d-q frame in theillustrated examples), and such values may include a d-axis componentand/or a q-axis component. In addition, certain values (e.g., theinverter output current feedback signals or values i_(u), i_(v), i_(w))may include signals or values corresponding to individual output phases(e.g., u, v, w) of a multiphase system, such as the inverter outputphases.

A summing junction 110 (FIG. 2) provides a speed or velocity errorsignal to a velocity proportional-integral (PI) controller 112 as thedifference between the desired velocity ω_(r)* and the motor velocitysignal or value ω_(r). Using the velocity PI controller component 112,the controller 100 thus calculates or otherwise determines one or morecurrent setpoint signals or values i_(dq)** (e.g., a d-axis value and aq-axis value in certain embodiments) at least partially according to thedesired motor velocity ω_(r)* and the motor velocity signal or valueω_(r). As mentioned above, although the illustrated example uses anouter velocity control loop, other implementations are possible in whicha torque setpoint or other setpoint(s) is/are used in controllingoperation of the motor load 20. Moreover, the concepts of the presentdisclosure may be employed in connection with other (non-motor) AC loads20 driven through an intervening filter circuit 30, wherein the invertercontroller 100 in such alternate embodiments may employ any suitabletype of setpoint and control algorithm, wherein the controller 100 neednot control velocity or position or torque in all embodiments.

The exemplary controller 100 in FIG. 2 further implements an innercurrent loop to control the inverter output currents i_(u), i_(v),i_(w). A current reference component 114 receives the d and q-axiscurrent setpoint signals or values i_(dq)** from the velocity PIcontroller 112, along with one or more signals or values I_(C) _(—)_(dq) representing the currents is flowing in the filter capacitorsC_(f) of the filter circuit 30. FIG. 3 illustrates further details ofone implementation of the current reference component 114, as well as afilter current calculation component 128 and a currentproportional-integral (PI) feed forward component 130 of the invertercontroller 100. As seen in FIG. 2, the current reference component 114provides compensated current setpoint values i*_(dq) to a summingjunction 116 based on the d and q-axis current setpoint values i**_(dq)and the filter capacitor current values I_(C) _(—) _(dq). The summingjunction 116, in turn, provides at least one error signal (e.g.,including d-axis and q-axis components) to a current PI controllercomponent 118 based on the difference between the compensated currentsetpoint values i*_(dq) and the d-q current feedback values i_(dq)obtained from a stationary/synchronous reference frame convertercomponent 132. The current PI control component 118 provides a controloutput as one or more voltage reference values v_(dq) to a summingjunction 120 to provide an inner voltage control loop implemented by thecontroller 100.

A summing junction component 120 computes or otherwise generates one ormore compensated voltage reference values v_(dq) _(—) _(ref) based onthe sum of the voltage reference values v_(dq) and feed forward voltagereference values V_(f) _(—) _(dq), and provides these to asynchronous/stationary reference frame converter component 122. Theconverter component 122 (and the stationary/synchronous reference frameconverter component 132) also receives a motor angle or position inputsignal or value θ_(r) (e.g., from a feedback sensor associated with themotor load 20 or derived from a position estimation algorithm, or fromanother suitable source) and the converter 122 converts the compensatedvoltage reference values v_(dq) _(—) _(ref) to provide 3-phase(stationary reference frame) voltage reference signals v_(uvw) to a PWMcomponent 124, which generates inverter switching control signals 102for operation of the switching devices S1-S6 of the inverter 46accordingly. The PWM component 124 may include suitable driver circuitryand/or other suitable hardware for generating switching control signals102 suitable for operating the switching devices S1-S6 as are known.

As further shown in FIG. 2, moreover, the illustrated invertercontroller 100 receives the speed/motor velocity signal or value ω_(r)and may optionally derive a scaled motor velocity signal or value ω_(e)from 126 as a function of an integer number P representing the number ofpole pairs of the driven motor load 20. A filter current calculationcomponent 128 receives the scaled motor velocity signal or value ω_(e)along with the compensated voltage reference signals or values v_(dq)_(—) _(ref), and provides the synchronous reference frame filtercapacitor current values I_(C) _(—) _(dq) for use by the currentreference component 114 as described above, as well as to a currentproportional-integral (PI) feed forward control component 130. CurrentPI feedforward component 130 receives the filter capacitor currentvalues I_(C) _(—) _(dq), the scaled motor velocity signal or valueω_(e), and the synchronous reference frame current feedback valuesi_(dq) as inputs, and determines the feedforward voltage referencevalues V_(f) _(—) _(dq) for provision to the summing junction component120 as described above. In operation, the controller 100 determines oneor more filter current or voltage signals or values representing afilter capacitor current (e.g., i_(C)) or filter inductor voltage (e.g.,v_(L)) of the filter circuit 30 based on at least one inverter outputfeedback signal or value (e.g., i_(u), i_(v), i_(w)) representing anoutput current at the AC output 46B of the inverter 46. The controller100, moreover, provides the inverter switching control signals 102 tothe inverter 46 at least partially according to the filter current orvoltage signal(s) or value(s).

The inventors have appreciated that the stationary reference frame (d-q)equations for a PM synchronous machines are given by the followingequation (1):

$\begin{matrix}{\begin{bmatrix}v_{md} \\v_{mq}\end{bmatrix} = {{\begin{bmatrix}{R_{s} + {\frac{\;}{t}L_{sd}}} & {{- \omega}\; L_{sq}} \\{\omega \; L_{sd}} & {R_{s} + {\frac{\;}{t}L_{sq}}}\end{bmatrix} \cdot \begin{bmatrix}i_{md} \\i_{mq}\end{bmatrix}} + {\omega \; {{\lambda_{pm}\begin{bmatrix}0 \\1\end{bmatrix}}.}}}} & (1)\end{matrix}$

In addition, cross coupling terms are introduced by the rotation fromthe stationary (uvw) reference frame to the synchronous (d-q) referenceframe, as seen in the following equation (2):

$\begin{matrix}\left. \frac{\lbrack x\rbrack_{abc}}{t}\Rightarrow{\frac{\lbrack x\rbrack_{dq}}{t} + {{\begin{bmatrix}0 & {- \omega} \\\omega & 0\end{bmatrix}\lbrack x\rbrack}_{dq}.}} \right. & (2)\end{matrix}$

Assuming the filter inductance L_(f) and capacitance C_(f) areconstants, and noting that motor volatges v_(m) equal to filter outputvoltages v_(f) _(—) _(out), the voltage across the inductor v_(L) isexpressed by the following equation (3):

$\begin{matrix}{{\begin{bmatrix}v_{Ld} \\v_{Lq}\end{bmatrix} = {{L_{f} \cdot {\frac{\;}{t}\begin{bmatrix}1 & 0 \\0 & 1\end{bmatrix}} \cdot \begin{bmatrix}i_{fd} \\i_{fq}\end{bmatrix}} + {\begin{bmatrix}0 & {{- \omega}\; L_{f}} \\{\omega \; L_{f}} & 0\end{bmatrix} \cdot \begin{bmatrix}i_{fd} \\i_{fq}\end{bmatrix}}}},} & (3)\end{matrix}$

and the capacitor current is expressed by the following equation (4):

$\begin{matrix}{\begin{bmatrix}i_{cd} \\i_{cq}\end{bmatrix} = {{C_{f} \cdot {\frac{\;}{t}\begin{bmatrix}1 & 0 \\0 & 1\end{bmatrix}} \cdot \begin{bmatrix}v_{{f\_ out}{\_ d}} \\v_{{f\_ out}{\_ q}}\end{bmatrix}} + {\begin{bmatrix}0 & {{- \omega}\; C_{f}} \\{\omega \; C_{f}} & 0\end{bmatrix} \cdot {\begin{bmatrix}v_{{f\_ out}{\_ d}} \\v_{{f\_ out}{\_ q}}\end{bmatrix}.}}}} & (4)\end{matrix}$

The inverter currents in the synchronous d-q reference frame are givenby the following equation (5):

$\begin{matrix}{\begin{bmatrix}i_{fd} \\i_{fq}\end{bmatrix} = {{\begin{bmatrix}i_{md} \\i_{mq}\end{bmatrix} + \begin{bmatrix}i_{cd} \\i_{cq}\end{bmatrix}} = {\begin{bmatrix}i_{md} \\i_{mq}\end{bmatrix} + {C_{f} \cdot {\frac{\;}{t}\begin{bmatrix}1 & 0 \\0 & 1\end{bmatrix}} \cdot \begin{bmatrix}v_{{f\_ out}{\_ d}} \\v_{{f\_ out}{\_ q}}\end{bmatrix}} + {\begin{bmatrix}0 & {{- \omega}\; C_{f}} \\{\omega \; C_{f}} & 0\end{bmatrix} \cdot \begin{bmatrix}v_{{f\_ out}{\_ d}} \\v_{{f\_ out}{\_ q}}\end{bmatrix}}}}} & (5)\end{matrix}$

In steady state, the inverter output currents (I_(fd) and I_(fq) in thesynchronous d-q reference frame) provided to the filter 30 are given bythe following equation (6):

$\begin{matrix}{{\begin{bmatrix}I_{fd} \\I_{fq}\end{bmatrix} = {\begin{bmatrix}I_{md} \\I_{mq}\end{bmatrix} + {\begin{bmatrix}0 & {{- \omega}\; C_{f}} \\{\omega \; C_{f}} & 0\end{bmatrix} \cdot \begin{bmatrix}v_{{f\_ out}{\_ d}} \\v_{{f\_ out}{\_ q}}\end{bmatrix}}}},} & (6)\end{matrix}$

including a first term representing the original motor currentreferences from the speed regulator (velocity PI controller 112), andthe final term showing the cross coupling terms in the inverter outputcurrent references taking into account the filter capacitor currents.The steady state inductor voltages V_(Ld) and V_(Lq) are given by thefollowing equation (7):

$\begin{matrix}{\begin{bmatrix}V_{Ld} \\V_{Lq}\end{bmatrix} = {{\begin{bmatrix}0 & {{- \omega}\; L_{f}} \\{\omega \; L_{f}} & 0\end{bmatrix} \cdot \begin{bmatrix}I_{fd} \\I_{fq}\end{bmatrix}} = {\quad{\begin{bmatrix}0 & {{- \omega}\; L_{f}} \\{\omega \; L_{f}} & 0\end{bmatrix} \cdot {\left( {\begin{bmatrix}I_{md} \\I_{mq}\end{bmatrix} + {\begin{bmatrix}0 & {{- \omega}\; C_{f}} \\{\omega \; C_{f}} & 0\end{bmatrix} \cdot \begin{bmatrix}v_{{f\_ out}{\_ d}} \\v_{{f\_ out}{\_ q}}\end{bmatrix}}} \right).}}}}} & (7)\end{matrix}$

In addition, the feedforward (FF) terms V_(f) _(—) _(dq) for the currentPI control component 118 including inductor voltages V_(Ld) and V_(Lq)in steady state, are given by the following equation (8):

$\begin{matrix}{{{\begin{bmatrix}V_{f\_ d} \\V_{f\_ q}\end{bmatrix}\begin{bmatrix}C & {{- \omega}\; L_{sq}} \\{\omega \; L_{sd}} & 0\end{bmatrix}} \cdot \begin{bmatrix}I_{md} \\I_{mq}\end{bmatrix}} + \begin{bmatrix}0 \\{\omega \; \lambda_{pm}}\end{bmatrix} + {\quad{\begin{bmatrix}0 & {\omega \; L_{f}} \\{\omega \; L_{f}} & 0\end{bmatrix} \cdot \left( {\begin{bmatrix}I_{md} \\I_{mq}\end{bmatrix} - {\begin{bmatrix}0 & {\omega \; C_{f}} \\{\omega \; C_{f}} & 0\end{bmatrix} \cdot \begin{bmatrix}v_{{f\_ out}{\_ d}} \\v_{{f\_ out}{\_ q}}\end{bmatrix}}} \right)}}} & (8)\end{matrix}$

including an original feedforward term as well as an additionalfeedforward term representing the inductor voltages V_(Ld) and V_(Lq).In this manner, the illustrated controller 100 employs a feedforwardinverter control scheme modified to incorporate the additional voltagesand currents associated with the filter circuit 30. To eliminate theneed to sense V_(f) _(—) _(out) _(—) _(dq), the controller can replaceV_(f) _(—) _(out) _(—) _(dq) with the compensated controller voltagesv_(dq) _(—) _(ref) in certain implementations.

FIG. 3 illustrates further details of non-limiting embodiments of thecurrent reference component 114, the filter current calculationcomponent 128, and the current PI feedforward control component 130, andFIG. 4 provides a flow diagram 200 depicting a control process 200 thatmay be implemented in the inverter controller 100. While the method 200of FIG. 4 is illustrated and described below in the form of a series ofacts or events, it will be appreciated that the various methods orprocesses of the present disclosure are not limited by the illustratedordering of such acts or events. In this regard, except as specificallyprovided hereinafter, some acts or events may occur in different orderand/or concurrently with other acts or events apart from thoseillustrated and described herein in accordance with the disclosure. Itis further noted that not all illustrated steps may be required toimplement a process or method in accordance with the present disclosure,and one or more such acts may be combined. The illustrated methods andother methods of the disclosure may be implemented in hardware,processor-executed software, or combinations thereof, in order toprovide the motor control and inverter control functionality describedherein, and may be employed in any power conversion system including butnot limited to the above illustrated PMSM drive 40, wherein thedisclosure is not limited to the specific applications and embodimentsillustrated and described herein.

A velocity loop proceeds at 202 (FIG. 4) and the controller 100 computescurrent setpoint values i**_(dq) at 204 based on the desired velocityvalue ω_(r)* and the motor velocity signal or value ω_(r), for example,using the summing junction component 110 and the velocity PI controller112 shown in FIG. 2. The current loop begins at 206, and the controllercomputes the filter capacitor current values I_(C) _(—) _(dq) at 208using the filter current calculation component 128 of FIG. 2, whichrepresents the current flowing in the filter circuit capacitor C_(f)based on the motor velocity signal or value ω_(r), the compensatedvoltage reference values v_(dq) _(—) _(ref), and the filter capacitancevalue C_(f). A non-limiting example of the filter current calculationcomponent 128 is further shown in FIG. 3, in which the d and q-axisfilter capacitor current components I_(C) _(—) _(d) and I_(C) _(—) _(q)are computed as a function of these values ω_(r), v_(dq) _(—) _(ref),and C_(f) using multiplier subcomponents 140 and 142 and a sign changecomponent 144 (e.g., multiply by −1) according to the above equation(4).

At 210 in FIG. 4, the controller 100 computes the compensated currentsetpoint values i*_(dq), based on the current setpoint values i**_(dq)and the filter capacitor current values I_(C) _(—) _(dq) using thecurrent reference component 114 (FIG. 2). As further shown in FIG. 3, anon-limiting embodiment of the current reference computation component114 is illustrated, which computes the compensated current setpointvalues i*_(dq) as a function of i**_(dq) and the d-q reference framefilter capacitor current values I_(C) _(—) _(d) and I_(C) _(—) _(q)received from the filter current calculation component 128 usingsummation components 146 and 148.

The compensated current reference setpoints (e.g., d and q axiscomponent values i*_(dq)) are then used as setpoints for the innervoltage control loops in FIG. 2 whereby the inverter switching controlsignals 102 are provided to the inverter 46 at least partially accordingto the compensated current setpoints i*_(dq). The controller 100computes voltage reference values V_(dq-ref) at 212-216 based on thecurrent PI feedforward control component 130 of FIGS. 2 and 3. As bestseen in FIG. 3, the current PI feedforward component 130 includessummation components 150, 156, 160 and 168, as well as multipliercomponents 152, 154, 162, 164 and 166, and a sign change component 158(e.g., multiply by −1) to implement the computation shown in the aboveequation (8). In the illustrated embodiment, the current PI feedforwardcontrol component 130 computes the feed forward voltage references V_(f)_(—) _(dq) in the synchronous reference frame at 214 based on theinverter output current feedback i_(dq), the motor velocity ω_(r) (e.g.,or the scaled value ω_(e)), the filter capacitor currents I_(C) _(—)_(dq), and the filter inductance value L_(f). The computed feed forwardvoltage references V_(f) _(—) _(dq) are then provided to the summingjunction 120 (FIG. 2) for computation of the compensated voltagereference values v_(dq) _(—) _(ref) (e.g., at 216 in FIG. 4) based onthe voltage reference values v_(dq) from the current PI controller 118and the feed forward voltage reference values V_(f) _(—) _(dq). At 218in FIG. 4, the controller 100 generates or otherwise provides theinverter switching control signals 102 to the inverter 46 at leastpartially according to the compensated voltage reference values V_(dq)_(—) _(ref):

In accordance with further aspects of the present disclosure, anon-transitory computer readable medium is provided, such as a computermemory, a memory within a power converter control system (e.g.,controller 100), a CD-ROM, floppy disk, flash drive, database, server,computer, etc.), which includes computer executable instructions forperforming the above-described methods. The above examples are merelyillustrative of several possible embodiments of various aspects of thepresent disclosure, wherein equivalent alterations and/or modificationswill occur to others skilled in the art upon reading and understandingthis specification and the annexed drawings. In particular regard to thevarious functions performed by the above described components(assemblies, devices, systems, circuits, and the like), the terms(including a reference to a “means”) used to describe such componentsare intended to correspond, unless otherwise indicated, to anycomponent, such as hardware, processor-executed software, orcombinations thereof, which performs the specified function of thedescribed component (i.e., that is functionally equivalent), even thoughnot structurally equivalent to the disclosed structure which performsthe function in the illustrated implementations of the disclosure. Inaddition, although a particular feature of the disclosure may have beendisclosed with respect to only one of several implementations, suchfeature may be combined with one or more other features of the otherimplementations as may be desired and advantageous for any given orparticular application. Also, to the extent that the terms “including”,“includes”, “having”, “has”, “with”, or variants thereof are used in thedetailed description and/or in the claims, such terms are intended to beinclusive in a manner similar to the term “comprising”.

The following is claimed:
 1. A power conversion system for driving aload through an intervening filter circuit, the power conversion systemcomprising: an inverter comprising a DC input, an AC output, and aplurality of switching devices coupled between the DC input and the ACoutput and operative according to inverter switching control signals toconvert DC electrical power received at the DC input to provide ACelectrical output power at the AC output; a controller configured todetermine at least one filter current or voltage signal or valuerepresenting a filter capacitor current or filter inductor voltage ofthe intervening filter circuit based on at least one inverter outputfeedback signal or value representing an output current at the AC outputof the inverter, and to provide the inverter switching control signalsto the inverter at least partially according to the at least one filtercurrent or voltage signal or value.
 2. The power conversion system ofclaim 1, wherein the controller is operative to: compute at least onecurrent setpoint value based on a desired velocity value and a motorvelocity signal or value; compute a filter capacitor current valuerepresenting current flowing in a filter capacitor of the interveningfilter circuit based on: the motor velocity signal or value, acompensated voltage reference value, and a filter capacitance value;compute a compensated current setpoint value based on the at least onecurrent setpoint value and the filter capacitor current value; andprovide the inverter switching control signals to the inverter at leastpartially according to the compensated current setpoint value.
 3. Thepower conversion system of claim 2, wherein the controller is operativeto: compute a voltage reference value based on the compensated currentsetpoint value, and at least one inverter output current feedback signalor value representing an output current at the AC output of theinverter; compute a feed forward voltage reference value based on the atleast one inverter output current feedback signal or value, the motorvelocity signal or value, the filter capacitor current value, and afilter inductance value; compute a compensated voltage reference valuebased on the voltage reference value, and the feed forward voltagereference value; and provide the inverter switching control signals tothe inverter at least partially according to the compensated voltagereference value.
 4. The power conversion system of claim 1, wherein thecontroller is operative to: compute a voltage reference value based on acompensated current setpoint value, and at least one inverter outputcurrent feedback signal or value representing an output current at theAC output of the inverter; compute a feed forward voltage referencevalue based on the at least one inverter output current feedback signalor value, a motor velocity signal or value, a filter capacitor currentvalue, and a filter inductance value; compute a compensated voltagereference value based on the voltage reference value, and the feedforward voltage reference value; and provide the inverter switchingcontrol signals to the inverter at least partially according to thecompensated voltage reference value.
 5. The power conversion system ofclaim 1, wherein the power conversion system is a motor drive, andwherein the inverter provides the AC electrical output power at the ACoutput to drive a motor load through the intervening filter circuit. 6.The power conversion system of claim 5, wherein the controller isoperative to: compute at least one current setpoint value based on adesired velocity value and a motor velocity signal or value; compute afilter capacitor current value representing current flowing in a filtercapacitor of the intervening filter circuit based on: the motor velocityvalue, a compensated voltage reference value, and a filter capacitancevalue; compute a compensated current setpoint value based on the atleast one current setpoint value and the filter capacitor current value;and provide the inverter switching control signals to the inverter atleast partially according to the compensated current setpoint value. 7.The power conversion system of claim 6, wherein the controller isoperative to: compute a voltage reference value based on the compensatedcurrent setpoint value, and at least one inverter output currentfeedback signal or value representing an output current at the AC outputof the inverter; compute a feed forward voltage reference value based onthe at least one inverter output current feedback signal or value, themotor velocity signal or value, the filter capacitor current value, anda filter inductance value; compute a compensated voltage reference valuebased on the voltage reference value, and the feed forward voltagereference value; and provide the inverter switching control signals tothe inverter at least partially according to the compensated voltagereference value.
 8. The power conversion system of claim 5, wherein thecontroller is operative to: compute a voltage reference value based on acompensated current setpoint value, and at least one inverter outputcurrent feedback signal or value representing an output current at theAC output of the inverter; compute a feed forward voltage referencevalue based on the at least one inverter output current feedback signalor value, a motor velocity signal or value, a filter capacitor currentvalue, and a filter inductance value; compute a compensated voltagereference value based on the voltage reference value, and the feedforward voltage reference value; and provide the inverter switchingcontrol signals to the inverter at least partially according to thecompensated voltage reference value.
 9. A method for controlling an ACelectric motor connected to a motor drive through an intervening filtercircuit, the method comprising: determining at least one filter currentor voltage signal or value representing a filter capacitor current orfilter inductor voltage of the intervening filter circuit based on atleast one motor drive output feedback signal or value representing anoutput current at an AC output of the motor drive; and generating ACelectrical output power at an AC output of the motor drive at leastpartially according to the at least one filter current or voltage signalor value.
 10. The method of claim 9, comprising: determining a filtercapacitor current value representing current flowing in a filtercapacitor of the intervening filter circuit based on: a motor velocitysignal or value, a compensated voltage reference value, and a filtercapacitance value; computing a compensated current setpoint value basedat least partially on the filter capacitor current value; and providinginverter switching control signals to an inverter of the motor drive atleast partially according to the compensated current setpoint value. 11.The method of claim 10, comprising: determining at least one currentsetpoint signal or value based at least partially on a desired motorvelocity and the motor velocity signal or value; and computing thecompensated current setpoint value based on the at least one currentsetpoint value and the filter capacitor current value.
 12. The method ofclaim 11, comprising: computing a voltage reference value based on thecompensated current setpoint value, and at least one inverter outputcurrent feedback signal or value representing an output current at theAC output of the inverter; computing a feed forward voltage referencevalue based on the at least one inverter output current feedback signalor value, the motor velocity signal or value, the filter capacitorcurrent value, and a filter inductance value; computing a compensatedvoltage reference value based on the voltage reference value, and thefeed forward voltage reference value; and providing the inverterswitching control signals to the inverter at least partially accordingto the compensated voltage reference value.
 13. The method of claim 12,comprising: receiving a plurality of motor drive output feedback signalsor values representing output currents at an AC output of the motordrive; determining d and q axis inverter output current feedback signalsor values in a stationary reference frame based at least partially onthe plurality of motor drive output feedback signals or values;computing the voltage reference value based on the compensated currentsetpoint value, and the d and q axis inverter output current feedbacksignals or values; and computing the feed forward voltage referencevalue based on the d and q axis inverter output current feedback signalsor values, the motor velocity signal or value, the filter capacitorcurrent value, and the filter inductance value.
 14. The method of claim9, comprising: computing a voltage reference value based on acompensated current setpoint value, and at least one inverter outputcurrent feedback signal or value representing an output current at theAC output of the inverter; computing a feed forward voltage referencevalue based on the at least one inverter output current feedback signalor value, a motor velocity signal or value, a filter capacitor currentvalue, and a filter inductance value; computing a compensated voltagereference value based on the voltage reference value, and the feedforward voltage reference value; and providing inverter switchingcontrol signals to an inverter of the motor drive at least partiallyaccording to the compensated voltage reference value.
 15. The method ofclaim 14, comprising: receiving a plurality of motor drive outputfeedback signals or values representing output currents at an AC outputof the motor drive; determining d and q axis inverter output currentfeedback signals or values in a stationary reference frame based atleast partially on the plurality of motor drive output feedback signalsor values; computing the voltage reference value based on thecompensated current setpoint value, and the d and q axis inverter outputcurrent feedback signals or values; and computing the feed forwardvoltage reference value based on the d and q axis inverter outputcurrent feedback signals or values, the motor velocity signal or value,the filter capacitor current value, and the filter inductance value. 16.A non-transitory computer readable medium with computer executableinstructions for controlling an AC electric motor connected to a motordrive through an intervening filter circuit, the computer readablemedium comprising computer executable instructions for: determining atleast one filter current or voltage signal or value representing afilter capacitor current or filter inductor voltage of the interveningfilter circuit based on at least one motor drive output feedback signalor value representing an output current at an AC output of the motordrive; and generating AC electrical output power at an AC output of themotor drive at least partially according to the at least one filtercurrent or voltage signal or value.
 17. The computer readable medium ofclaim 16, comprising computer executable instructions for: determining afilter capacitor current value representing current flowing in a filtercapacitor of the intervening filter circuit based on: a motor velocitysignal or value, a compensated voltage reference value, and a filtercapacitance value; computing a compensated current setpoint value basedat least partially on the filter capacitor current value; and providinginverter switching control signals to an inverter of the motor drive atleast partially according to the compensated current setpoint value. 18.The computer readable medium of claim 17, comprising computer executableinstructions for: determining at least one current setpoint signal orvalue based at least partially on a desired motor velocity and the motorvelocity signal or value; and computing the compensated current setpointvalue based on the at least one current setpoint value and the filtercapacitor current value.
 19. The computer readable medium of claim 18,comprising computer executable instructions for: computing a voltagereference value based on the compensated current setpoint value, and atleast one inverter output current feedback signal or value representingan output current at the AC output of the inverter; computing a feedforward voltage reference value based on the at least one inverteroutput current feedback signal or value, the motor velocity signal orvalue, the filter capacitor current value, and a filter inductancevalue; computing a compensated voltage reference value based on thevoltage reference value, and the feed forward voltage reference value;and providing the inverter switching control signals to the inverter atleast partially according to the compensated voltage reference value.20. The computer readable medium of claim 16, comprising computerexecutable instructions for: computing a voltage reference value basedon a compensated current setpoint value, and at least one inverteroutput current feedback signal or value representing an output currentat the AC output of the inverter; computing a feed forward voltagereference value based on the at least one inverter output currentfeedback signal or value, a motor velocity signal or value, a filtercapacitor current value, and a filter inductance value; computing acompensated voltage reference value based on the voltage referencevalue, and the feed forward voltage reference value; and providinginverter switching control signals to an inverter of the motor drive atleast partially according to the compensated voltage reference value.